The independent particle approximation is shown to break down for the photoionization of both inner and outer nᐉ ͑ᐉ . 0͒ electrons of all atoms, at high enough energy, owing to interchannel interactions with the nearby ns photoionization channels. The effect is illustrated for Ne 2p in the 1 keV photon energy range through a comparison of theory and experiment. The implications for x-ray photoelectron spectroscopy of molecules and condensed matter are discussed. [S0031-9007 (97)03382-6] PACS numbers: 32.80.Fb
Angular distributions of valence photoelectrons showing effects due to highermultipole photon interactions have been measured for the first time. Neon 2s and 2p photoemission exhibits effects beyond the dipole approximation throughout the 250-1200 eV photon-energy range studied. The results suggest that any photoemission experiment, on any sample, can be affected at relatively low photon energies, pointing to a general need for caution in interpreting angle-resolved-photoemission measurements.
Calculations of the cross section, angular distribution asymmetry parameter and photoelectron spin-polarization parameters for valence photoionization of neutral beryllium using the relativistic-random-phase approximation plus relativistic-multichannel quantum defect theory are performed in the region of Rydberg resonances just below the 1s ionization threshold. A new autoionizing series, 1s2s2np 3P, which occurs solely due to relativistic effects, is found. A quantitative study of the character of resonances has been carried out and the implications of these relativistic resonances for angular distributions and spin polarization are investigated in detail.
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